WRRC SeminarJune 20, 3:00pm - 4:00pm
Mānoa Campus, WATANABE 112
Importance of sub-surface rhizosphere-mediated coupled nitrification-denitrification in a flooded agroecosystem in Hawaii
C. Ryan Penton, Postdoctoral Research Associate, Center for Microbial Ecology, Michigan State University
The fate of fertilizer nitrogen (N) in flooded agroecosystems is difficult to predict given the multitude of potential N transformation pathways. In particular, rhizosphere effects are known to play a significant role in N cycling, but are especially difficult to quantify in large emergent macrophytes. To address these issues, we utilized a whole core 15NH4+ perfusion technique with porewater equilibrators for the extraction of 14/15N-NO3-, NH4+, and N2 coupled with quantification of N cycling genes through the sediment column. Sub-surface denitrification was found to be an important N loss pathway in wetland sediments vegetated with aerenchymatous taro (Colocasia esculenta) versus bare sediments. Driven by hypothesized thermo-osmotic mechanisms linked to photosynthesis, diurnal O2 transport into the sub-surface stimulated nitrification-denitrification in the extensive root rhizosphere. Overall we wereable to account for >82% of added 15NH4+ in the vegetated cores over a ten-day incubation through both plant incorporation and surface/sub-surface coupled nitrification-denitrification. In summary, these results suggested (1) that oxygen flux through the taro stem and root system into the flooded sediment may be an important driver of nitrification and coupled denitrification in these systems, and (2) that oxygen flux is mediated by air movement (wind) and the diurnal light-cycle related to photosynthesis.
Water Resources Research Center, Mānoa Campus
Philip Moravcik, (808) 956-3097, firstname.lastname@example.org